CN112650336A - Cracking furnace repeating crossbow control system and method - Google Patents

Abstract

The invention provides a cracking furnace repeating crossbow control system, which comprises: one or more by-pass hydrocarbon feed flow control modules FB_iConfigured to control by-pass hydrocarbon feed flow FSV_i(ii) a One or more branch outlet temperature control modules TB_iA variable quantity TC configured to control the bypass hydrocarbon feed flow_i(ii) a Fuel gas flow control module FB_GFor controlling the incoming fuel gas flow FC_G(ii) a And a cracking furnace outlet COT temperature control module T_COTWith said fuel gas flow control module FB_GForming a cascade control loop. The invention also relates to a cracking furnace crossbow control method, which effectively reduces the fluctuation of branch temperature in the operation process and the load adjustment process of the cracking furnace and improves the overall operation stability of the cracking furnace.

Description

Cracking furnace repeating crossbow control system and method

Technical Field

The invention relates to the field of petrochemical industry, in particular to a cracking furnace crossbow control system and method.

Background

The cracking furnace is the core equipment of the production device of byproducts such as ethylene, propylene and the like, cracking raw materials are preheated and then are often divided into a plurality of branches to enter the cracking furnace, the existing cracking furnace has complex process and easy coking, and when the operation temperature is high (more than 820 ℃), the products are distributed in a nonlinear way. In addition, the ethylene production device often needs to increase and decrease the load, and the change of the feeding amount of the cracking raw material directly influences the stable operation of the COT temperature and the branch temperature in the process of increasing and decreasing the load.

Therefore, the invention provides a cracking furnace branch balancing system and a cracking furnace branch balancing method with a brand-new concept, and the system and the method are called as a cracking furnace repeating crossbow control system and a method. The repeating crossbow control thought is from a weapon which is manufactured by Zhuge Liang in the period of three nations and can shoot a plurality of arrows at the same time. In an ethylene production device, in order to reduce the pressure drop of a furnace tube and save energy, raw materials are heated uniformly, and cracking raw materials are preheated and then are often divided into a plurality of branches to enter a cracking furnace. The invention introduces the idea that the repeating crossbows shoot a plurality of arrows at the same time into the control scheme of the cracking furnace, and establishes a cracking furnace repeating crossbow control system.

When the load is kept unchanged, based on the principle of heat transfer, the temperature of each branch is taken as a measured value, the furnace outlet temperature (COT) is taken as a set value, a branch temperature controller is established, the output of the branch temperature controller is taken as the raw material flow adjustment amount required by the branch, the flow of each branch of the cracking furnace is redistributed under the condition of ensuring that the load is unchanged, the branch with high branch temperature increases the feeding amount, the branch with low branch temperature reduces the feeding amount, and the outlet temperature of each branch is ensured to be as close as possible.

When the load of the cracking furnace changes, repeating crossbow control is carried out on each branch at the same time to adjust the feeding amount, and the load adjustment is realized on the premise of ensuring the flow balance of each branch.

Disclosure of Invention

Aiming at the technical problems in the prior art, the invention discloses a cracking furnace crossbow control system, which comprises: one or more by-pass hydrocarbon feed flow control modules FB_iConfigured to control by-pass hydrocarbon feed flow FSV_i(ii) a One or more branch outlet temperature control modules TB_iA variable quantity TC configured to control the bypass hydrocarbon feed flow_i(ii) a Fuel gas flow control module FB_GFor controlling the incoming fuel gas flow FC_G(ii) a And COT temperature control module T_COTWith said fuel gas flow control module FB_GForming a cascade control loop.

Further, the repeating crossbow control system, wherein said one or moreBranch outlet temperature control module TB_iCorresponding to one or more branch outlet temperatures T_OUTi。

Further, the repeating crossbow control system further comprises a calculation module configured to calculate one or more branch feed adjustment increment and STC_HPDAnd decrement and STC_HPRWherein the increment is

Wherein the decrement is

Furthermore, the repeating crossbow control system also comprises limit values STC of the adjustment quantity of each branch_DREWherein STC_DRE＝min(STC_HPD,abs(STC_HPR) ); the delta and STC_HPDFurther comprising a delta coefficient C_HPDIn which C is_HPD＝STC_DRE/STC_HPD(ii) a The decrement and STC_HPRFurther comprises a decrement coefficient C_HPRIn which C is_HPR＝STC_DRE/STC_HPR。

Further, the repeating crossbow control system, wherein the limit value STC of each branch adjusting quantity_DREThe single maximum increment or maximum decrement is DSV; wherein, a single maximum adjustment increment or maximum adjustment decrement DF is also included_BLAnd a single adjustment coefficient C_BL；DF_BL＝min(STC_DRE,DSV)，C_BL＝DF_BL/STC_DRE(ii) a Wherein, the method also comprises the single adjustment DFSV of branch feeding quantity_i，

The by-pass hydrocarbon feed flow FSV_i＝FSV_i+DFSV_i。

Furthermore, the repeating crossbow control system also comprises a cracking furnace total load set value QSV, wherein the QSV is QSV₀+ Δ QSV · t. QSV therein₀Is the initial set value of the load of the cracking furnace, and the delta QSV is the load adjustment speed of the cracking furnaceThe rate, t, is the time of load adjustment, the by-pass hydrocarbon feed flow

Further, the repeating crossbow control system and the COT control module T_COTThe temperature control range of (1) is 700-900 ℃.

The invention discloses a cracking furnace crossbow control method, which comprises the following steps: controlling by-pass hydrocarbon feed flow FSV_i(ii) a Variation TC of control branch hydrocarbon feed flow_i(ii) a Controlling incoming fuel gas flow FC_G(ii) a And forming a cascade control loop.

Further, the repeating crossbow control method calculates the feed adjustment increment of one or more branches and STC_HPDAnd decrement and STC_HPRWherein the increment is

Wherein the decrement is

Further, the repeating crossbow control method also comprises limit STC of each branch adjusting quantity_DREWherein STC_DRE＝min(STC_HPD,abs(STC_HPR) ); the delta and STC_HPDFurther comprising a delta coefficient C_HPDIn which C is_HPD＝STC_DRE/STC_HPD(ii) a The decrement and STC_HPRFurther comprises a decrement coefficient C_HPRIn which C is_HPR＝STC_DRE/STC_HPR。

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description in the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a block diagram of a cracking furnace repeating crossbow control system according to one embodiment of the present invention;

FIG. 2 is a block diagram of a cracking furnace repeating crossbow control module according to an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of a repeating crossbow control system of an ethylene cracking furnace according to another embodiment of the present invention;

FIG. 4 is a graph of temperature and flow rate operation of the ethylene cracking furnace with crossbow control before implementation in accordance with the embodiment of the present invention shown in FIG. 3;

FIG. 5 is a graph of temperature and flow operating curves after the ethylene cracking furnace crossbow control of the embodiment of FIG. 3 has been implemented, in accordance with the present invention;

fig. 6 is a flowchart of a method for controlling a crossbow in a pyrolysis furnace according to one embodiment of the present invention.

Reference numerals:

101-a cracking furnace; 102-a repeating crossbow control module;

103-first branch hydrocarbon feed flow; 103' -ith branch hydrocarbon feed flow;

104-a first branch hydrocarbon feed flow control module; 104' -the ith branch hydrocarbon feed flow control module;

105-a first branch outlet temperature control module; 105' -the ith branch outlet temperature control module;

106-first branch outlet temperature; 106' -ith branch outlet temperature;

107-COT temperature control module; 108-fuel gas flow;

109-fuel gas flow control module; 201-a cracking furnace crossbow controller;

301-ethylene cracking furnace; 302-a first branch flow controller;

303-a second branch flow controller; 304-a third branch flow controller;

305-a fourth branch flow controller; 312-first branch outlet temperature controller;

313-a second branch outlet temperature controller; 314-third branch outlet temperature controller;

315-fourth branch outlet temperature controller; 306-COT temperature controller;

307-fuel gas flow controller; 308-fuel gas flow.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the following detailed description, reference is made to the accompanying drawings that form a part hereof and in which is shown by way of illustration specific embodiments of the application. In the drawings, like numerals describe substantially similar components throughout the different views. Various specific embodiments of the present application are described in sufficient detail below to enable those skilled in the art to practice the teachings of the present application. It is to be understood that other embodiments may be utilized and structural, logical or electrical changes may be made to the embodiments of the present application.

The technical solution of the present invention is further illustrated by a specific example. It should be understood by those skilled in the art that the following descriptions are only for convenience in understanding the technical solutions of the present invention and should not be used to limit the scope of the present invention.

Fig. 1 is a block diagram of a cracking furnace repeating control system according to an embodiment of the present invention. As shown in the figure, there are n sets of feed flows of the cracking furnace, and the cracking furnace 101 repeating crossbow control system includes a repeating crossbow control module 102, a first branch hydrocarbon feed flow 103, an ith branch hydrocarbon feed flow 103', a first branch hydrocarbon feed flow control module 104, an ith branch hydrocarbon feed flow control module 104', a first branch outlet temperature control module 105, an ith branch outlet temperature control module 105', a first branch outlet temperature 106, an ith branch outlet temperature 106', COT temperature control module 107, fuel gas flow control module 108, fuel gas flow 109. Wherein, the first branch hydrocarbon feed flow control module 104 and the ith branch hydrocarbon feed flow control module 104' are one or more branch hydrocarbon feed flow control modules FB_iConfigured to control the corresponding branch hydrocarbon feed flow FSV_iNamely a first branch hydrocarbon feed flow 103 and an ith branch hydrocarbon feed flow 103'.

The input of the COT temperature control module is connected with a COT temperature measuring instrument, the input of the feed flow control module is connected with a flow measuring instrument, and the output of the feed flow control module is sent to the branch flow regulating valve. The input of the fuel gas flow control module is connected with a fuel gas flow measuring instrument, and the output is sent to a fuel gas flow regulating valve. The temperature control module related to the invention can be provided with a temperature measuring instrument, wherein the temperature measuring instrument can be of a contact type or a non-contact type, and comprises but is not limited to a thermal resistor, a thermocouple and the like. Those skilled in the art will appreciate that the above are just a few types of temperature control modules. Alternative existing temperature control modules known in the art may also be used herein.

The flow control module of the present invention may be selected from flow meters, including but not limited to differential pressure flow meters, rotameters, electromagnetic flow meters, etc. Those skilled in the art will appreciate that the above are just a few types of flow control modules. Alternative existing flow control modules known in the art may also be used herein.

Referring to fig. 1, the repeating crossbow control system of the cracking furnace 101 according to one embodiment of the present invention includes a first branch outlet temperature control module 105 and an ith branch outlet temperature control module 105' which are one or more branch outlet temperature control modules TB_iA variable quantity TC configured to control the bypass hydrocarbon feed flow_i. Pyrolysis furnace 101 fuel gas flow control module FB _G108 for controlling the fuel gas flow FC into the cracking furnace 101_G109. 101COT temperature control module T of cracking furnace _COT107 which is in fuel gas flow control module FB with the cracking furnace 101_G108 form a cascaded control loop. Flow control module by fuel gasFB _G108 regulating fuel gas flow FC _G109 to effect adjustment of the temperature of the COT.

105, 105' one or more branch outlet temperature control modules TB as shown in FIG. 1_iCorrespondingly comprising 106, 106' one or more branch outlet temperatures T_OUTi. The adjusting method of repeating crossbow control comprises the steps of increasing feeding flow of branches with high branch temperature and reducing feeding flow of branches with low branch temperature. For a single branch, if the outlet temperature of the branch is higher than the COT, the inlet temperature of the branch cannot be adjusted, and the heat absorbed by the branch needs to be shared by increasing the flow of the branch, so that the outlet temperature is reduced to approach the COT. According to the heat conservation principle and the heat transfer rate equation, the following expression is given:

Q＝Cp×FSV_i×(T_OUTi-T_COT)＝Cp×TC_i×(T_COT-T_INi) (1)

wherein TCi is the variation of the hydrocarbon feed flow of the branch which needs to be adjusted in the ith branch, FSVi is the hydrocarbon feed flow 103' of the branch, Q represents the sum of the heat quantity transmitted before and after the adjustment, and T_INiIs the inlet temperature, T, of the ith branch of the cracking furnace_OUTiIs the outlet temperature 106' of the ith branch of the cracking furnace_COTThe cracking furnace COT temperature is 107.

The repeating crossbow control system further comprises a calculating module, wherein the calculating module is used for calculating increment and decrement sum of one or more branch feeding adjusting amount, and the following expressions are provided:

in the formula, STC_HPDIndicating branch feedIncrement of the whole quantity and, STC_HPRRepresenting the decrement sum of the bypass feed adjustment.

According to the feeding amount, the limit value of the adjustment amount of each branch and the corresponding STC can be further calculated_HPDDelta coefficient of delta sum, STC_HPRThe decrement coefficient of the decrement sum is specifically as follows:

STC_DRE＝min(STC_HPD,abs(STC_HPR)) (5)

C_HPD＝STC_DRE/STC_HPD (6)

C_HPR＝STC_DRE/STC_HPR (7)

STC_DRElimiting the adjustment of each branch, C_HPDAs a branch increment factor, C_HPRIs the branch decrement coefficient.

Wherein, the limit value STC of each branch adjusting quantity in the repeating crossbow control system is set_DREThe single maximum increment or maximum decrement is DSV, and the allocation relationship is as follows:

DF_BL＝min(STC_DRE,DSV) (8)

C_BL＝DF_BL/STC_DRE (9)

DF in formula_BLFor single maximum adjustment increments or maximum adjustment decrements, C_BLIs a single adjustment factor. Single adjustment of each branch feeding DFSV_iComprises the following steps:

final adjusted branch hydrocarbon feed flow FSV for each branch_i103' is:

FSV_i＝FSV_i+DFSV_i (11)

when the load of the whole cracking furnace changes, the set value of the total load of the cracking furnace is assumed to be QSV-QSV₀+ Δ QSV · t, then per branch hydrocarbon feed flow FSV_i103' is calculated as:

according to one embodiment of the invention, the COT control module T of the cracking furnace_COTThe temperature control range of 107 is 700-900 ℃.

Fig. 2 is a structural diagram of a cracking furnace repeating crossbow control operation module according to an embodiment of the invention. As shown, a furnace crossbow controller 201 is used to read the furnace branch inlet temperature T_INiOutlet temperature T_OUTiAnd a bypass feed flow FV_iSingle maximum increment or maximum decrement DSV of each branch adjusting flow, initial set value QSV of cracking furnace load₀Cracking furnace load adjustment rate Δ QSV, time t of load adjustment;

setting single branch single maximum adjustment increment and STC (coefficient of performance) as shown in figures 1 and 2_HPDWith maximum adjustment decrement and STC_HPR. According to the principle of controlling the repeating crossbow of the cracking furnace, a repeating crossbow control module 102 is developed on a DCS, and is loaded and debugged in a control system. Calculating to obtain the adjustment DFSV of each branch by a repeating crossbow control module_i. Finally, the initial set value QSV of the load of the cracking furnace is read₀The load adjustment rate delta QSV of the cracking furnace and the load adjustment time t are calculated according to the repeating crossbow control module 102 to obtain the set value FSV of the branch flow controller_i。

Compared with the traditional control method, the cracking furnace crossbow control method has the following advantages that: aiming at the problem that the temperature of the outlet of each branch in the normal operation process and the load adjustment process of the cracking furnace has deviation, the heat balance before and after adjustment is kept based on the principle of heat balance, the repeating crossbow control method of the cracking furnace is provided, the feeding amount of each branch is adjusted at the same time, the purpose of reducing the temperature fluctuation of the branch is realized, the temperature fluctuation of the branch in the operation process and the load adjustment process of the cracking furnace is effectively reduced, and the overall operation stability of the cracking furnace is improved.

Fig. 3 is a schematic structural diagram of a repeating crossbow control system of an ethylene cracking furnace according to another embodiment of the present invention. As shown, the ethylene-cracking furnace 301 has four feed streams. Wherein the first branch flow controller 302,The second branch flow controller 303, the third branch flow controller 304 and the fourth branch flow controller 305 are used to control the branch hydrocarbon feed flow FSV_i. Wherein the first branch outlet temperature controller 312, the second branch outlet temperature controller 313, the third branch outlet temperature controller 314 and the fourth branch outlet temperature controller 315 are used for controlling the branch outlet temperature T_OUTi. Wherein the hearth COT temperature 306 is T_COT. Fuel gas flow controller 307FB_GConfigured to control fuel gas flow 308FC_G。

Fig. 4 is a graph illustrating temperature and flow rate operation before the ethylene cracking furnace crossbow control according to the embodiment of the present invention shown in fig. 3 is performed, and fig. 5 is a graph illustrating temperature and flow rate operation after the ethylene cracking furnace crossbow control according to the embodiment of the present invention shown in fig. 3 is performed.

Referring to FIGS. 3, 4 and 5, the furnace inlet feeds are provided with FIC101, FIC201, FIC301 and FIC401 respectively representing a first branch flow controller 302, a second branch flow controller 303, a third branch flow controller 304 and a fourth branch flow controller 305, TIC101, TIC201, TIC301 and TIC401 representing a first branch outlet temperature controller 312, a second branch outlet temperature controller 313, a third branch outlet temperature controller 314 and a fourth branch outlet temperature controller 315, TIC001 representing a furnace COT temperature controller 306 and FIC001 representing a fuel gas flow controller 307. Because the combustion temperature in the cracking furnace is unevenly distributed, the branch temperature is different, therefore, a cracking furnace crossbow control module is developed, the maximum adjustment increment/decrement of a single branch per minute is set to be 0.1 ton, when the single branch runs for 100 minutes, the load is reduced by 4 tons, when the single branch runs for 200 minutes, the load is increased by 4 tons, and the branch temperature is loaded and implemented in a DCS system, so that the aim of reducing the branch temperature difference is fulfilled.

As shown in fig. 4 and 5, before the repeating control of the cracking furnace, the COT temperature and the four branch feeds fluctuate within a small range around the set value, and both the COT temperature and the four branch feeds fluctuate as the load of the cracking furnace decreases and increases. After the repeating crossbow control is implemented, under the normal operation condition and when the load of the cracking furnace is reduced and increased, the COT temperature and the temperature operation curves of the four branches are stable, the feeding fluctuation of the branches is also reduced to some extent, and the stable operation of the whole cracking furnace is facilitated.

Fig. 6 is a flowchart of a method for controlling a crossbow in a pyrolysis furnace according to one embodiment of the present invention.

In step 610, the bypass hydrocarbon feed flow is controlled. As previously described, according to embodiments of the present invention, controllability of flow volume is achieved using one or more by-pass hydrocarbon feed flow control modules.

In step 620, the amount of change in the bypass hydrocarbon feed flow rate is controlled. Quantification of branch hydrocarbon feed flow temperature data is achieved by one or more branch outlet temperature control modules.

In step 630, the incoming fuel gas flow is controlled. As previously described, the fuel gas flow rate is controlled using a fuel gas flow control module.

In step 640, a cascade control loop is formed. A cascade control loop can be formed by the COT temperature control module and the fuel gas flow control module.

The above embodiments are provided for illustrative purposes only and are not intended to limit the present invention, and various changes and modifications may be made by those skilled in the relevant art without departing from the scope of the present invention, and therefore, all equivalent technical solutions should fall within the scope of the present disclosure.

Claims (10)

1. A cracking furnace crossbow control system comprising:

one or more by-pass hydrocarbon feed flow control modules FB_iConfigured to control by-pass hydrocarbon feed flow FSV_i；

One or more branch outlet temperature control modules TB_iA variable quantity TC configured to control the bypass hydrocarbon feed flow_i；

Fuel gas flow control module FB_GFor controlling the incoming fuel gas flow FC_G(ii) a And

COT temperature control module T_COTWith said fuel gas flow control module FB_GForming a cascade control loop.

2. The system of claim 1, wherein the one or more branch outlet temperature control modules TB_iIncluding one or more branch outlet temperatures T_OUTi。

3. The system of claim 1, further comprising a calculation module configured and arranged to calculate one or more leg feed adjustment delta and STC_HPDAnd decrement and STC_HPR，

Wherein the increment is

Wherein the decrement is

4. The system of claim 3 further comprising a limit STC for each leg adjustment_DREWherein STC_DRE＝min(STC_HPD,abs(STC_HPR))；

The delta and STC_HPDFurther comprising a delta coefficient C_HPDIn which C is_HPD＝STC_DRE/STC_HPD；

The decrement and STC_HPRFurther comprises a decrement coefficient C_HPRIn which C is_HPR＝STC_DRE/STC_HPR。

5. The system of claims 1 and 4 wherein the limit STC for each leg adjustment amount_DREThe single maximum increment or maximum decrement is DSV;

wherein, a single maximum adjustment increment or maximum adjustment decrement DF is also included_BLAnd a single adjustment coefficient C_BL；DF_BL＝min(STC_DRE,DSV)，C_BL＝DF_BL/STC_DRE；

Wherein, the method also comprises the single adjustment DFSV of branch feeding quantity_i，

The by-pass hydrocarbon feed flow FSV_i＝FSV_i+DFSV_i。

6. A system according to claim 5, further comprising a cracking furnace total load setpoint QSV, QSV-QSV₀+ Δ QSV · t. QSV therein₀Is the initial set point of the furnace load, Δ QSV is the rate of furnace load adjustment, t is the time of load adjustment, and the branch hydrocarbon feed flow rate

7. The system of claim 1, the COT control module T_COTThe temperature control range of (1) is 700-900 ℃.

8. A cracking furnace crossbow control method comprises the following steps:

controlling by-pass hydrocarbon feed flow FSV_i；

Variation TC of control branch hydrocarbon feed flow_i；

Controlling incoming fuel gas flow FC_G(ii) a And forming a cascade control loop.

9. The method of claim 7 calculating one or more leg feed adjustment delta and STC_HPDAnd decrement and STC_HPR，

Wherein the increment is

Wherein the decrement is

10. The method of claim 8 further comprising a limit STC for each leg adjustment_DREWherein STC_DRE＝min(STC_HPD,abs(STC_HPR))；

The delta and STC_HPDFurther comprising a delta coefficient C_HPDIn which C is_HPD＝STC_DRE/STC_HPD；

The decrement and STC_HPRFurther comprises a decrement coefficient C_HPRIn which C is_HPR＝STC_DRE/STC_HPR。

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